A military vehicle aboard an overloaded plane in broke free and struck critical operating systems, probably leading to the 2013 crash that killed all seven crew members, US safety officials said on Tuesday.
The National Transportation Safety Board said an improperly secured mine-resistant, ambush-protected vehicle, known as an MRAP, went through the bulkhead and disabled two hydraulic systems, making the aircraft uncontrollable.
The Dubai-bound Boeing 747-400 plane crashed just after takeoff from Bagram airbase on 29 April 2013, killing six crew members. It was operated by National Air Cargo Group Inc and carried 207 tonnes of cargo, including five MRAPs, weighing between 12 and 18 tonnes each.
NTSB officials found “critical safety deficiencies”, including a failure by National Air Cargo, which does business as National Airlines, to restrain cargo.
Investigators also found inadequate federal aviation administration (FAA) oversight of cargo operator procedures and inspector training, as well as unclear responsibility for the oversight of special cargo-handling operations.
National Airlines did not immediately comment. The FAA said it would officially respond within the required 90 days, and that officials have reviewed air-carrier manuals and guidance on cargo loading, operations and other procedures at National Airlines and other cargo carriers.
The NTSB had said in February that it was examining shifting cargo as a possible factor. The plane had picked up the five vehicles at Camp Bastion, Afghanistan, and had taken on 53 tonnes of fuel at Bagram before taking off for Dubai.